1. Field of the Invention
The present invention relates to a transmission including a positioning means for positioning a reverse shifting fork, swingably supported on a reverse shifting fork holder, in a reverse position and neutral position.
2. Description of the Related Art
Such a transmission has been proposed, for example, in Japanese Patent Application No. 11-295418 filed by the present applicant. This transmission includes a fifth-speed/reverse shifting rod capable of being swung to a reverse position and a fifth-speed position through a neutral position set therebetween. The movement of the fifth-speed/reverse shifting rod between the neutral position and the reverse position is transmitted through a cam mechanism to a reverse shifting fork. The fifth-speed/reverse shifting rod is adapted to be appropriately stopped in any of the neutral position, the reverse position and the fifth-speed position by a detent mechanism. The detent mechanism includes a ball biased by a spring and three recesses into each of which the ball can be fitted, and the reverse shifting fork is positioned indirectly in any of the neutral position and the reverse position through the detent mechanism.
However, even if the fifth-speed/reverse shifting rod is positioned by the detent mechanism, since a transmitting member such as a cam mechanism is interposed between the fifth-speed/reverse shifting rod and the reverse shifting fork, an accumulated unevenness in the transmitting path of the transmitting member causes insufficient positioning of the reverse shifting fork. Therefore, the reverse shifting fork has been conventionally positioned directly in any of the neutral position and the reverse position by disposing a second detent mechanism between the reverse shifting fork and a reverse shifting fork holder for swingably supporting the reverse shifting fork.
The conventional second detent mechanism is comprised of a ball held in a retaining bore in the reverse shifting fork holder, two recesses which are defined in the reverse shifting fork and into each of which the ball can be fitted, and a leaf spring mounted on the reverse shifting fork holder for biasing the ball in a direction to fit the ball into each of the recesses in the reverse shifting fork. As such, the conventional second detent mechanism has a complicated structure, resulting in not only an increased weight and cost, but also the generation of a large frictional force between the ball and the reverse shifting fork, and a reduced shift operability.
The present invention has been accomplished with such circumstances in view, and it is an object of the present invention to provide a transmission having a simplified structure with fewer parts in order that a reverse shifting fork can be positioned reliably in any one of a reverse position and a neutral position, providing a smooth shift operability between the reverse position and the neutral position.
To achieve the above object, there is provided a transmission, comprising a positioning means for positioning a reverse shifting fork swingably supported on a reverse shifting fork holder in a reverse position and a neutral position. The positioning means includes a toggle spring for biasing the reverse shifting fork toward one of the reverse position and the neutral position with a dead point set as a boundary between the reverse position and the neutral position. A first stopper means stops the reverse shifting fork in the reverse position against a biasing force of the toggle spring. A second stopper means stops the reverse shifting fork in the neutral position against the biasing force of the toggle spring.
With the above arrangement, the reverse shifting fork is biased by the toggle spring toward one of the reverse position and the neutral position with the dead point set as the boundary between the reverse position and the neutral position, and the reverse shifting fork biased by the toggle spring is stopped in the reverse position and the neutral position by the first and second stopper means, respectively. Therefore, the structure of the positioning means of the present invention is simplified, leading to a reduction in the weight and cost of the positioning means, over the positioning means of the conventional detent mechanism. Furthermore, the reverse shifting fork of the present invention moved beyond the dead point can be quickly swung into the reverse position or the neutral position by the toggle spring, thereby providing a preferable and appropriate smooth shift operability between the reverse position and the neutral position.
The toggle spring of the present invention comprises a torsional coil spring, which is compressed so that a biasing force is generated in a direction to move opposite ends of the spring connected respectively to the reverse shifting fork holder and the reverse shifting fork away from each other. The distance between the opposite ends of the spring is smallest in the dead point.
With the above arrangement, the toggle spring comprises the torsional coil spring connected at its opposite ends to the reverse shifting fork holder and the reverse shifting fork. As a result, the structure of the positioning means can be greatly simplified.
A torsional coil spring 91 in an embodiment corresponds to the toggle spring of the present invention; a first stopper face 50c and a stopper pin 92 in the embodiment correspond, in cooperation with each other, to the first stopper means of the present invention; and a second stopper face 50d and the stopper pin 92 in the embodiment correspond, in cooperation with each other, to the second stopper means of the present invention.